In the manufacture of semiconductor wafers and integrated circuits, metal films are deposited on semiconductor substrates, oxides and other dielectrics. These metal films are used for different purposes, such as forming interconnect lines, metallic contacts, conductive vias and other conductive features on and above various surfaces of the semiconductor wafers.
Typically, aluminum has been a preferred conductive metal because it avoids various problems, such as a high contact resistance with silicon, which normally accompanies the use of gold and copper. Copper also suffers drawbacks compared to aluminum because copper migrates into device areas, causing problems in device performance. Aluminum, on the other hand, has good adhesion to silicon dioxide and performs well with plasma etching, as compared to copper.
Recently, greater interest has been shown by manufacturers of semiconductor devices in the use of copper and copper alloys for metallization patterns, such as in conductive vias and interconnects. Copper, compared to aluminum, has both good electromigration resistance and a relatively low electrical resistivity of about 1.7 .mu.ohm.multidot.cm. Unfortunately, copper is relatively quick to oxidize and/or corrode especially during processing or manufacturing of the integrated circuit. For example, after chemical mechanical polishing (CMP), localized corrosion of the copper conductor may occur when hydrofluoric acid (HF) attacks the barrier layer and copper conductor. HF is typically used in the cleaning step for removal of copper and slurry particulates from the oxide/dielectric surface by chemical etching.